A strong quake struck off northern Chile on Sunday evening, triggering a preventive evacuation of part of the coastal area but not causing any injuries or damage to the country's crucial copper mines.

The magnitude 6.7 quake, originally measured as a 7.0, was centred 60km west-northwest of Iquique and hit at a depth of 20km, the US Geological Survey said.

The USGS said a second quake that hit about 10 minutes later registered a preliminary magnitude of 5.1.

The ONEMI emergency office said that preliminarily no damage or injuries had been reported after the shake, which struck at 6.16pm local time (10.16am NZT).

Chile's massive mines, clustered in the mineral-rich North, appeared to be fine. Collahuasi, a partnership between Glencore Xstrata and Anglo American, located in the area, said operations were normal.

The Pacific Tsunami Warning Center said there was no tsunami expected.

But Chile's navy said there was a possibility of what it called ''a minor tsunami,'' so authorities ordered a preventive evacuation of part of the coastline after the quake.

''Everything indicates that (the seriousness of the situation) will diminish,'' said Ricardo Toro, director of the ONEMI.

He said a ''small tsunami'' refers to sea level rises no bigger than a negligible 32 centimeters. Local media showed footage of people in Iquique calmly evacuating on foot to nearby hills.